This invention relaters generally to material delivery systems and more particularly to a material delivery system for delivering solid materials such as particles, granules or powders over an extended range of material delivery rates.
The concept of feeders such as vibratory feeders and gravity feeders are known in the art. In the vibratory feeder, solid material is fed into one end of a horizontal vibrating trough and discharges from the other end as the vibrating action drives the material from one end of the horizontal trough to the other end where the material is discharged. By controlling the amount of vibration applied to the trough and the amount of material delivered to the trough the rate of material fed from the trough can be controlled. Similarly, in an air-activated gravity feeder, where the trough or chute is located at an angle, the solid material flows from the upper end of a chute to the lower end of a chute as air is blown upward through the solid material to fluidize the material. By control of the amount of air supplied to the air-activated gravity feeder and the amount of material delivered to the air-activated gravity feeder the rate of material delivered from the air-activated gravity feeder can be controlled. Both such type of feeders are useful in the handling and delivering of solid materials in measurable rates from one location to another. One of the drawbacks of such systems is that the range of the rate of material delivery for a particular feeder is limited. Typically, prior art feeders can have a xe2x80x9cturndown rangexe2x80x9d of about eight to one. By xe2x80x9cturndown rangexe2x80x9d it is understood to mean the ratio of the maximum amount of material a feeder can deliver at a controlled or uniform rate in relation the minimum amount of material a feeder can deliver at a controlled or uniform rate. For example, with a turndown range of eight to one the maximum amount the system can deliver at a controlled or uniform rate is eight units per minute and the minimum amount of material that the feeder can deliver at a controlled or uniform rate is one unit per minute. While the xe2x80x9cturndown rangexe2x80x9d varies from machine to machine and from material to material a characteristic of such feeders is that the range of the rate of delivery of materials that can be fed is limited as one cannot uniformly throttle down the rate of delivery of solid particles like one can throttle down the flow of fluid with a metering valve. This makes it difficult to use vibratory feeders or air-activated gravity feeders for ladling out materials to weigh scales as uneven flow can cause to much material to be delivered. Consequently, to handle different flow rates at uniform type flow rates multiple feeders having different capacity are often used in the same system in order to obtain the necessary range of rate of delivery of material. The present invention provides an attachment that can increase the xe2x80x9cturndown rangexe2x80x9d from eight to one to one thousand to one while maintaining a substantially uniform material delivery rate. As a result one size feeder can be used in a variety of different applications.
U.S. Pat. No. 5,767,455 discloses a typical vibratory feeder for delivering material from one location to another location.
Dynamic Air specification bulletin 9806 discloses an air-activated gravity conveyor that can be built with various size conveying chambers.
Briefly, the invention comprises an attachment for a air-activated gravity or vibratory feeder with the attachment comprising an angularly postionable gate that is angularly postionable within the trough of a feeder with the postionable gate having a secondary metering outlet so that when the postionable gate is in the down position it partially close off the material flow path within the feeder while allowing a portion of the solid materials in the material flow path to pass therethrough to thereby extend the range of rates at which material can be controllable and uniformly delivered from the feeder.